Multicolored etched polytetrafluoroethylene sheet

ABSTRACT

An etched polytetrafluoroethylene sheet is made having at least one non-white color pigmented portion and at least one unpigmented etch monitor control portion.

United States Patent 1191 Rosenblatt, Jr. et al.

[ Sept. 3, 1974 MULTICOLORED ETCHED POLYTETRAFLUOROETHYLENE SHEET Inventors: Girard B. Rosenblatt, Jr., Los Altos; Donald C. Wold, Sunnyvale, both of Calif.

Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: Aug. 23, 1972 Appl. No.: 283,256

US. Cl 161/164, 156/2, 161/160, 161/189, 252/795 1111. c1. B231) Field of Search 156/2, 307, 308; 252/795; 117/47 A; 161/116, 160, 164, 189

[56] References Cited UNITED STATES PATENTS 3,115,536 12/1963 Janis et al. 156/2 X 3,205,113 9/1965 McFarland 156/7 X Primary Examiner-William A. Powell Attorney, Agent, or FirmD. P. Cillo [5 7] ABSTRACT An etched polytetrafluoroethylene sheet is made having at least one non-white color pigmentedportion and at least one unpigmented etch monitor control portion.

6 Claims, 1 Drawing Figure ETCH MONITOR CONTROL PORTION OF THE SHEET i ETCHED SHEET PAIENIEDSEP Y 3;a33;455

ETCHED ETCH MONITORK CONTROL PORTION OF THE SHEET MULTICOLORED ETCHED POLYTETRAFLUOROETHYLENE SHEET The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Navy.

BACKGROUND. OF THE INVENTION The missile launching tubes on submarines require a shock absorbing and launch dynamics control liner to prevent damage to the missile in the case of pitching and rolling in rough seas, from near misses by depth charges while the vessel is submerged, and to control the launch dynamics. This liner is currently in the form of shaped, cast urethane pads (upper liner) or molded neoprene rubber pads (lower liner). White tetrafluoroethylene tape is usually adhered on the inside diameter of the pads to reduce missile-pad interface friction. The bonding side of the tape is chemically etched to obtain a bondable surface, since untreated tetrafluoroethylene will not bond well with adhesives.

It has long been known that electromagnetic radiation, including ultraviolet, degrades the chemical etching on tetrafluoroethylene. Thus, separation of the tape from the liner can occur after long periods of liner exposure to sunlight, as when the launch tube hatch is left open. One'remedy for avoiding the effects of sunlight on the tape is to incorporate an ultraviolet radiation absorber, such as carbon black pigment, with the powdered white polytetrafluoroethylene resin during the manufacturing process. This would provide a black pigmented tape, essentially opaque to ultraviolet radiation. However, the use of black pigmented tape does not allow monitoring of the etching process.

The most widely accepted surface treatment to improve bondabilityof polytetrafluoroethylene sheet is to etch the sheet in a solution of sodium metal and liquid ammonia, as described in US. Pat. No. 2,789,063, or in a bath consisting of an alkali metal polyaryl hydrocarbon solvent solution as described in US. Pat. No.

'A specified quality control check for procurement of uniformly and reproducibly etched polytetrafluoroethylene is to employ Federal Color Specification No. 595, to compare the etched surface with predetermined color parameters. There is a need then for a method of making a polytetrafluoroethylene etched tape that will be color pigmented and yet allow monitoring of the etching process.

SUMMARY OF THE INVENTION An etched polytetrafluoroethylene sheet having at least one non-white color pigmented portion and at least oneintegral unpigmented etch monitor control portion, is made by mixing a pigment with polytetrafluoroethylene particles to provide a colored mixture,

placing the colored mixture into a mold to provide a layer and placing unpigmented polytetrafluoroethylene particles into the mold to provide another layer, compressing the layers to provide a shape having separate layers, curing the shape, shaving the shape to provide a sheet having a colored portion and an integral etch monitor control unpigmented portion, and etching the sheet to provide a color change in at least the etch monitor control portion of the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be made to the preferred embodiment, exemplary of the invention, shown in the accompanying drawing, which shows a method of shaving or skiving a cured multicolored billet of polytetrafluoroethylene, to provide a flexible multicolored sheet, having an integral etch monitor control portion disposed lengthwise along an edge of the sheet,'and etching one side of the sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS over which the mixture is placed. The mixture of pigment and polytetrafluoroethylene is then compressed, after which regular white polytetrafluoroethylene particles can .be added on top of the compressed pigmented polytetrafluoroethylene, and the regular white particles compressed in the mold. In this way a single top or bottom white layer, or alternating white and pigmented layers are provided in the mold.

It is preferred that each layer of particles be individually compressed to about 10 to 50 percent of its uncompressed volume, so that individual strata will be formed with a definite interface.

- The compressed'shape cross section will generally be in rectangular or circular form. In the rectangular compressed shape, individual stiff or flexible sheets can easily be shaved off with a white control portion disposed along one edge, whereas the circular billet molding lends itself easily to a continuous long sheet roll manufacturing process.

Preferably, the pigmented polytetrafluoroethylene is loaded into a cylindrical mold and compressed in the axial. direction. White polytetrafluoroethylene is poured on top and similarly compressed to form a multicolored cylindrical billet containing compacted strata of white and colored polytetrafluoroethylene.

The billet can then be processed by sintering the particles in the mold, or more often the billet is removed from the mold andcured in an oven.

The billet, shown as 10 in the drawing, is then cooled and comprises, as in the case where about 0.3 to 5.0 weight percent carbon black pigment is added to make the final tape substantially opaque to ultraviolet radiation, a white stratum 11, about 1 to 3 in. wide, and a black pigmented stratum 12, of suitable width, having a definite black white interface 13.

A multicolored, flat, flexible polytetrafluoroethylene sheet 14 can then be shaved or skived from the billet by a suitable means. For example a movable sharp edge knife blade 15, contacting the billet along its length and placed parallel to the billet axis, can be used to provide a thin flexible sheet 14 of a desired thickness, which can be continuously shaved and drawn from the billet. This sheet 14 comprises a white, unpigmented portion 16 and a pigmented portion 17 with a definite interface 18 between the portions. Generally, the white portion 16, which is the integral unpigmented monitor control section, to insure proper etching of the polytetrafluoroethylene tape, will be disposed lengthwise along one edgeof the sheet. It will be about l-3 in. wide, to allow easy removal, if desirable, after etching tests have been run. Different color pigmented polytetrafluoroethylene layers can be incorporated into the pigmented billet strata, to provide multicolor portions in the pigmented part of the skived sheet, with white control portions disposed between the colored portions or along one or both edges of the sheet. I

The sheet 14 may then be rolled up and subsequently etched or passed through. asuitable etching means 19, effective to etch only one side of the sheet, directly after the shaving step. Suitable surface .treatment would be to contact one side of the sheet with an effective etchant as by spraying,'painting or contact with a rotating drum partially submerged in the'etchant. A protective resist couldalso be applied to one side and the tape passed through an etchant bath. Suitable etchants include, for example, a solution of alkali metal in liquid ammonia or an alkali metal polyaryl hydrocarbon solvent solution. During etching, the surface of the white monitor control portion of the sheet will turn a dull brown to black color. The etched sheet 20 can then be quality control checked to insure that the desired degree of etching has been attained, bycomparing the color of the integral etched monitor control portion 21 of the sheet with predetermined color parameters using, for example, Federal Color Specification 595.

This method provides a multicolored etched polytetrafluoroethylene (PTFE) sheet, having an integral, small, easily removable portion which readily shows the degree of etching of the polytetrafluoroethylenesurface. ln many instances 200 to 500 feet of sheet must be inspected to insure adequate uniformity of etching.

This method can provide a sheet capable of meeting such rigorous quality control standards. After the requisite color inspection the etched monitor control portion 21 of the sheet can be cutoff by any suitable means if desired.

Suitable adhesives for use with the etched polytetrafluoroethylene sheet include polyurethane resin systems and epoxy resin systems among others.

A variety of polytetrafluoroethylene billets were made containing 0.5-1.5 percent by weight of carbon black and 10 mil thick by about 18 in. wide sheets were made from them by a lathe technique. The black pigmented P'T FE powder was added to the cylindrical mold first to avoid light colored oc culsions in the final dark tape. It is very important to have a definite interface between the portions otherwise monitoring is difficult, and an excessive waste of PTFE occurs since you have to cut deeply into the sheet to get to an all black portion. The mold was about 1 ft. in diameter and 6 ft. long, and the black pigmented PT FE powder was filled almost to the mold top. About 4 in. of regular white PTF E powder between about 175 and 450 microns average particle diameter was then added. The column was compressed to about 20 percent of its volume with minimum disturbance of the black white interface.

The billet was removed from the mold'and cured in an oven at about 300 to 350 C. After being skived, the sheet had a black portion about 16 in. wide and a definite integral, white monitor control section about 2 in. wide. One side of the sheet was etched in a solution of sodium metal and liquid ammonia. The black portion etched surface remained black giving no indication of any surface change but the etched side of the control section turned from a dull white-grey color to brown, confirming that the tape had been etched. Subsequently, samples of the etched sheet were bonded to polyurethane foam backing layers with a polyurethane resin adhesive and were found to effectively resist delamination caused by ultraviolet radiation.

We claim:

1. A flexible polytetrafluoroethylene sheet having one etched side, the sheet having a pigmented portion, resistant to ultraviolet radiation consisting essentially of polytetrafluoroethylene and about 0.3 to 5.0 weight percent carbon pigment, and an integral etch monitor control portion, consisting essentially of unpigmented polytetrafluoroethylene.

2. The polytetrafluoroethylene sheet of claim 1 wherein the etch monitor control portion is disposed lengthwise along an edge of the sheet and there is a definite interface between the portions of the sheet.

3. A polytetrafluoroethylene sheet having one etched side, the sheet having at least one non-white color pigmented portion comprising polytetrafluoroethylene and pigment, and at least one integral etch monitor control portion comprising unpigmented polytetrafluoroethylene.

4. The polytetrafluoroethylene sheet of claim 3 wherein the etch monitor control portion is disposed lengthwise along at least one edge of the sheet.

5. The polytetrafluoroethylene sheet of claim 3 wherein at least one etch monitor control portion is disposed between color pigmented portions of the sheet.

of the sheet. 

2. The polytetrafluoroethylene sheet of claim 1 wherein the etch monitor control portion is disposed lengthwise along an edge of the sheet and there is a definite interface between the portions of the sheet.
 3. A polytetrafluoroethylene sheet having one etched side, the sheet having at least one non-white color pigmented portion comprising polytetrafluoroethylene and pigment, and at least one integral etch monitor control portion comprising unpigmented polytetrafluoroethylene.
 4. The polytetrafluoroethylene sheet of claim 3 wherein the etch monitor control portion is disposed lengthwise along at least one edge of the sheet.
 5. The polytetrafluoroethylene sheet of claim 3 wherein at least one etch monitor control portion is disposed between color pigmented portions of the sheet.
 6. The polytetrafluoroethylene sheet of claim 3 wherein there is a definite interface between the pigmented portions of the sheet and the control portions of the sheet. 